The interfacial microenvironment of micelles, mixed micelles and vesicles will be investigated using polarity-sensitive spectroscopic probes. The effect of this local microenvironment on dissociation constants of indicator dyes will be studied. Some recent theories of solubilization in micellar systems will be tested by comparing the solubilization capacities of micelles and vesicles for aromatic solutes with the solubilities of the aromatic solutes in hydrocarbons.